What should a corpsman do if a patient has an allergic reaction?

When a patient experiences an allergic reaction, administering antihistamines, if available, is the appropriate course of action. Antihistamines are designed to counteract the effects of histamines released during an allergic response, which can alleviate symptoms such as itching, hives, and nasal congestion. This intervention is crucial as it can help stabilize the patient's condition and prevent the reaction from worsening.

In cases of known allergies, especially when symptoms are moderate to severe, having antihistamines readily available is an essential component of emergency preparedness in medical settings. It is important to respond promptly to allergic reactions as they can escalate quickly and lead to more serious complications, like anaphylaxis.

While other options might provide some comfort to the patient, they do not directly address the allergic reaction's physiological response. For instance, ignoring the situation can lead to more severe symptoms, while allowing rest or encouraging deep breathing exercises may not provide the necessary medical intervention to mitigate the allergic response effectively. Thus, administering antihistamines is the most appropriate response to manage an allergic reaction.